1. Field of the Invention
The present invention relates to an optical semiconductor device in which an optical semiconductor element including a light-receiving or light-emitting portion is accommodated.
2. Description of the Related Art
Since circuit devices to be set in electronic equipment are used in a mobile phone, a portable computer, and the like, there has been a demand for reduction in size, thickness and weight of the circuit devices. Taking a semiconductor device as an example of the circuit devices, chip size packages (CSP) have been developed. The size of CSP is equal to chip size or, slightly larger than a chip size.
FIG. 7 shows a CSP 66 with a size slightly larger than a chip size, in which a glass epoxy substrate 65 is employed as a supporting substrate. A description will be given here assuming that a transistor chip T is mounted on the glass epoxy substrate 65.
First and second electrodes 67, 68 and a die pad 69 are formed on a surface of this glass epoxy substrate 65, and first and second back electrodes 70 and 71 are formed on a back of the glass epoxy substrate 65. The first electrode 67 and first back electrode 70, as well as the second electrode 68 and second back electrode 71, are electrically connected through a through-hole TH. The bare transistor chip T is fixed to the die pad 69. An emitter electrode of the transistor and the first electrode 67 are connected by a thin metal wire 72, and a base electrode of the transistor and the second electrode 68 are connected by another thin metal wire 72. Moreover, a resin layer 73 is provided on the glass epoxy substrate 65 so as to cover the transistor chip T.
Although the glass epoxy substrate 65 is used in the CSP 66, the CSP 66, unlike a wafer scale CSP, has a simple elongating structure from the transistor chip T up to the back electrodes 70 and 71 for external connection, and therefore has a merit of being able to be manufactured at low costs.
In the CSP 66 explained above, however, the resin layer 73 covering the transistor chip T is only in contact with a surface portion of the glass epoxy substrate 65. Accordingly, during the process of mounting the CSP 66 and/or in the state where the CSP 66 is being used, water enters from the outside into the interface between the glass epoxy substrate 65 and the resin layer 73. This fact has led to degradation in the moisture resistance of the CSP 66. Moreover, from the same reason as above, there has been a problem of weak adhesion between the glass epoxy substrate 65 and the resin layer 73.